In a heavy saucepan, combine sugar, corn syrup and vinegar. Cook
over medium heat, stirring constantly, until sugar dissolves. Cook
without stirring until the temperature reaches 300 (hard crack
stage) on a candy thermometer. Do not overcook.

Remove from the heat and quickly stir in baking soda. Pour into a
buttered 13-in. x 9-in. x 2-in. baking pan. When cool, break into
bite size pieces. Dip into melted chocolate; place on waxed paper
until the chocolate is firm.